Use BackupHandler from tf_slim instead of OD API's clone.

PiperOrigin-RevId: 323916181

research/object_detection/data_decoders/tf_example_decoder.py

@@ -124,40 +124,6 @@ class _ClassTensorHandler(slim_example_decoder.Tensor):
                       self._display_name_to_id_table.lookup(unmapped_tensor))
 
 
-class _BackupHandler(slim_example_decoder.ItemHandler):
-  """An ItemHandler that tries two ItemHandlers in order."""
-
-  def __init__(self, handler, backup):
-    """Initializes the BackupHandler handler.
-
-    If the first Handler's tensors_to_item returns a Tensor with no elements,
-    the second Handler is used.
-
-    Args:
-      handler: The primary ItemHandler.
-      backup: The backup ItemHandler.
-
-    Raises:
-      ValueError: if either is not an ItemHandler.
-    """
-    if not isinstance(handler, slim_example_decoder.ItemHandler):
-      raise ValueError('Primary handler is of type %s instead of ItemHandler' %
-                       type(handler))
-    if not isinstance(backup, slim_example_decoder.ItemHandler):
-      raise ValueError(
-          'Backup handler is of type %s instead of ItemHandler' % type(backup))
-    self._handler = handler
-    self._backup = backup
-    super(_BackupHandler, self).__init__(handler.keys + backup.keys)
-
-  def tensors_to_item(self, keys_to_tensors):
-    item = self._handler.tensors_to_item(keys_to_tensors)
-    return tf.cond(
-        pred=tf.equal(tf.reduce_prod(tf.shape(item)), 0),
-        true_fn=lambda: self._backup.tensors_to_item(keys_to_tensors),
-        false_fn=lambda: item)
-
-
 class TfExampleDecoder(data_decoder.DataDecoder):
   """Tensorflow Example proto decoder."""
 
@@ -405,12 +371,12 @@ class TfExampleDecoder(data_decoder.DataDecoder):
     if label_map_proto_file:
       # If the label_map_proto is provided, try to use it in conjunction with
       # the class text, and fall back to a materialized ID.
-      label_handler = _BackupHandler(
+      label_handler = slim_example_decoder.BackupHandler(
           _ClassTensorHandler(
               'image/object/class/text', label_map_proto_file,
               default_value=''),
           slim_example_decoder.Tensor('image/object/class/label'))
-      image_label_handler = _BackupHandler(
+      image_label_handler = slim_example_decoder.BackupHandler(
           _ClassTensorHandler(
               fields.TfExampleFields.image_class_text,
               label_map_proto_file,